Lightning arrester



United States Patent O LIGHTNING ARRESTER Ralph R. Pittman, Little Rock, Ark. Application April 7, 1958, Serial No. 726,853 8 Claims. (Cl. 313-231) This invention relates generally to lightning protective devices adapted for use in connection with energized electrical circuits for the purpose of limiting the voltage rise which may be impressed on an associated conductor by lightning strokes or otherwise.

An object of the present invention is the provision of a voltage-responsive device capable of discharging transient surge currents and at the same time preventing the ignition of a dynamoelectric power-follow current arc along the path followed by the surge current through the device.

A further object is the provision of a protective device embodying insulating members arranged to contain a surge-discharge spark, the bounding insulating members being so relatively movable under the conditions of operation as to compensate for any erosion of the insulating members which may result from the passage of the surge-discharge current and the associated gas blast, thereby providing a device having the ability to repeatedly discharge surge-currents without destroying the geometrical relationship of the insulating members essential to the proper operation of the device.

Another object of the invention resides in the provision of means for compensating for the changes in the dimensions of the insulating members bounding the discharge path associated with changes in weather conditions, particularly humidity, so that the ability of the device to accept surge current and reject power-follow current is runaffected by its atmospheric environment.

The single figure of the drawing illustrates a preferred embodiment of the invention.

The particular embodiment shown in the drawing is a lightning arrester having a discharge chamber within the tubular insulator 20, hard fiber being one material suitable for the Construction of the latter. An upper electrode 16,`here shown as an inverted cup-shaped metal member, is threaded into and closes the upper end of the tubular insulator 20, and the metal upper-terminal stud '12 threadedly extends downward through the top portion and into the holl'ow of the upper electrode 16.

In somewhat similar manner, a lower metal electrode 22 extends upwardly from the lower end of the tubular insulator 20 into and in threaded engagement therewith, the upper end of the lower electrode 22 being spaced from the lower end of the upper electrode 16 to provide a spark gap therebetween for a discharge spari; along the smooth inner cylindrical surface of the tubular insulator 20.

A metal lower terminal stud 26 extends coaxially upward in threaded engagement with the lower electrode member 22, an outwardly extending threaded portion of the stud 26 being provided with the terminal nuts 27 and 28, for c'onvenience in connecting a ground wire thereto, and for use in mounting the device, if desired. The vents 23 provide for the escape of gas which may be expanded or generated within the tubular insulator 20, and the sleeve 25 encloses a portion of the terminal stud 26 to provide protection from possible damage which might attend gas discharge.

An elongated conically tapered member of insulating material 18, having a smooth outer surface, extends coaxially within the tubular insulator 20, in spaced relationship with the inner smooth surface =thereof. 'The member 18 is fixed in position through the engagement of its conically-enlarged end with an upper portion 24 of the lower electrode 22, and its conically-reduced end is positioned near the upper electrode 16. Hard fiber is a suitable material for the Construction of the tapered member 18.

A helically-formed member of insulating material 19, which may also be of hard fiber, is slidably mounted on the tapered member 18, for longitudinal movement therealong, and between the electrodes 16 and 22 in slip-fit frictional engagement With both its outer smooth surface and the inner smooth surface of the tubular insulator 20. The land of the spiral of the helical member 19 is tapered outward from its abutment with the conically formed member 18 to its abutment with the inner surface of the tubular insulator 20, so that the contact-area of the helical member 19 abutting the conical member 18 is substantially larger than that abutting the inner surface of the tubular insulator 20, thereby insuring that sparkover occurring between the respective adjacent portons of the electrodes 16 and 22 will be along the inner surface of the tubular insulator 20. A helical spring 17 is coaxially disposed between the upper electrode 16 and the upper end of the helical member 19, being arranged to continuously urge the latter downward between the conical member 18 and the inner surface of the tubular insulator 20.

The size and shape of the three insulating members constituting the discharge structure, namely, the tube 20, the conical member 18, and the relatively movable helical member 19, are important to the proper operation of the device in connection with alternating current circuits, being directly related to the R.M.S. 60 cycle voltage of the circuit to which the device is applicd. As an illustration, an arrester according to the invention herein operates successfully in connection with a 60 cycle, 8 kv. crcuit with a sparkover path (shortest distance between electrodes) about 5 inches in length, the internal diameter of the tubular insulator being about one inch, the inner conical member tapering from about /4 inch diameter at its lower end to /2 inch diameter at its upper end over a length of about 5 inches, and the land of the helical member being about 24 inches long, inch wide externally and inch wide internally. This is the construction shown in the drawing in approxmate actual size.

A housing 21, of glass, porcelain or similar weatherproof insulating material, is provided to house the members of the discharge structure, 'being supported at its lower end by the outwardly extending flange :of the lower electrode 22, and positioned and covered at its upper end by the metal cover 14, the latter being fixed in position by the nut 13 of the stud 12. Gaskets 15 and 29 are provided to seal the joints at the ends of the housing 21.

In applying the device, the upper terminal 10 is connected to the normally energized terminal of a device to be protected, the external series spark gap 11 being provided in accordance with common prac 'ce to avoid possible damage resulting from leakage current which might otherwise be passed through the device. The lower terminal 26 is usually connected to ground.

When so connected, upon the occurrence of a predetermined excess voltage, such as might be caused by lightning, the gap 11 along with the internal gap between the electrodes 16 and 22 sparks over, discharging the surge to ground. The discharge spark follows a path along 3 the outer surface of the intermediate member 19 and the inner surface of the tubular insulator 20. The heat attending the dscharge eXpands the air within the discharge structure, and this expansion, along with any gaseous distillation products from the fiber members, exerts a downward pressure which moves the intermediate helical member in the direction to expand and thus wedge it tigltly between theinner conical member and the tubular insulator, thereby so increasng the dielectric strength of the device that the kindling of a dynamoelectric 60 cycle follow-current arc is precluded over the path broken down by the discharge spark. The longer spiral path from one electrode to the other, 'because of its length, also refuses to accept follow-current, with the result that the device operates selectively as a conductor for discharging transient surge currents and as an insulator with respect to the normal voltage condition which prevails immediately following the surgecurrent discharge.

The convoluted spiral passage of the member 19 between the electrodes is efiective to prevent longitudinal grooving along the discharge path, and instead provides for uniform erosion `over the outer surface of the land and the inner surface of the tubular insulator 20. While such erosion is usually very small during a single operaton, it is nevertheless important that the slip-fit surface abutment be continuously maintained to assure proper operation, because only a very slght longitudnal opening or crack will destroy the effectiveness of the device by allowing it to accept arcs energized from the 60 cycle impressed voltage.

Any loss of insulating material accompanying an operation being uniform over the involved surfaces, it is only necessary to uniformly expand the helical member 19 to fill any void produced by such loss to enable the device to perform properly when the next operation occurs. This is accomplished by constructing the member 19 'of such material and dimensions that it is flexibly and uniformly expanded in diameter as it is moved downwa'd either under the influence of the spring 17 or the pressure applied by the gas attending each discharge spark.

Certain insulating material, particularly hard fiber, of which the members 18, 19, and 20 may be constructed, shrink when losing moisture and expand when absorbing moisture. To maintain the desired slip-t relationship of these members under Varying atmospheric humidity conditions, the spring 17 is provided for continuously urgng the helical member 19 downward to assure that it remains properly seated during wet-dry weather cycles.

It will be apparent from the foregoing description that modifications and variations of the present invention are possible, and that it may be practice/d otherwise than as specifically described and illustrated.

I claim, as my invention:

1. In a lightning arrester having an outer tubular insulator closed :at one end and vented at the other end and spaced conducting electrodes associated therewith for ,causing sparkover to occur therein; a fixed inner member of insulating material conically reduced at the closed end of said tubular insulator and extending coaxially in spaced relationship therein, a relatively movable intermediate helical member of insulating material slidably mounted on said fixed inner member in slip-fit frictional engagement with the respective adjacent surfaces of said inner member and said outer tubular insulator, :and spring means biasing said movable helical member toward the vented end of said tubular insulator.

2. A lightning arrester comprising an outer tubular insulator closed at the upper end and vented at the lower end, said insulator having a smooth inner cylindrical surface and spaced conducting upper and lower electrodes associatedtherewith, at least one of said electrodes extending endwise into said tubular insulator for establishing a sparkover path therein, an inner conical member of insulating material having a smooth outer surface engaging 'the lower electrode and tapering coaxially toward face of the land of said helical member engaging the inner smooth surface of said tubular insulator to assure the establishment of a sparkover path along the smooth inner surface :of said tubular insulator, and spring means urging said intermediate helical member downwardly toward the lower electrode.

3. A lightning arrester comprising an outer tubular insulator closed at the upper end and vented at the lower end, said insulator having a smooth inner cylindrical surface and spaced conducting upper and lower electrodes associated therewith, at least one of said electrodes extending endwise into said tubular insulator for establishing a sparkover path therein, an inner conical member of insulating material engagng the lower electrode and tapering coaxially toward the uppe'r electrode, an intermediate helical member of insulating material slidably disposed between said electrodes in frictional slip-fit engagement with the adjacent surfaces of said inner member and said tubular insulator, and spring means urging said intermediate helical member downwardly toward the lower electrode.

4. A lightning arrester comprising an outer tubular insulator closed at the upper end and vented at the lower end, said insulator having a smooth inner cylindrical surface and spaced conducting upper and lower electrodes extendng into its respective ends for establishing a sparkover path along said smooth inner surface, an inner conical member of insulating material engagng the lower electrode and tapering coaxially toward the upper electrode, an intermediate helical member of insulating material slidably disposed between said electrodes in frictional slip-fit engagement with the adjacent surfaces of said inner member and said tubular insulator, and spring means urging said intermediate helical member downwardly toward the lower electrode.

5. A lightning arrester comprising a tubular insulator closed at one end and vented at the other end, spaced conducting electrodes extending into the respective' ends of said tubular insulator for establishing a sparlgover path therebetween along the inner surface of said tubular ini sulator, a fixed inner conical member of insulating material tapering from the vented end toward the closed end of said tubular insulator, and a spirally-formed intermediate member of insulating material slidably mounted on said inner member in slip-fit engagement with the adjacent surfaces of said inner member and said tubular insulator between the adjacent portions of said electrodes.

6. A lightning arrester comprising a tubular insulator closed at one end and vented at the other end, spaced conducting electrodes extending into the respective ends of said tubular insulator for establishing a sparkover path therebetween along the inner surface of said tubular insulator, a fixed inner member of insulating material conically reduced near the closed end of said tubular insulator, and an intermediate helical member of insulating material extending around saidinner member in slip-fit abutting engagement with the adjacent surfaces of said inner member and said tubular insulator between the adjacent portions of said electrodes.

7. A lightning arrester comprising a tubular insulator closed at one end and vented at the other end, spaced conducting electrodes extending into the respective ends of said tubular insulator for establishing a sparkover path therebetween along the inner surface of said tubular insulator, a fixed inner conical member of insulating material tapering from the vented end toward the closed end of said. tubular insulator, a spirally-formed intermediate member of nsulating material extend'ng around and slidably movable along said inner member in slp-fit engagement with the adjacent surfaces of said inner member and said tubular insulator between the adjacent portions of said electrodes, and spring means urging said intermediate member toward the vented end of said tubular insulator.

8. In a lightning arrester having an outer tubular insulator closed at one end and vented at the other end and spaced conducting electrodes associated therewith for causing sparkover to occur therein; a fixed inner member of nsulating material conically reduced at the closed end of said tubular insulator and extending coaxially in spaced relationship therein, a relatively longitudnaliy movable and flexibly expansible intermediate helical u 2,69L742 member of insulating material slidably mounted on said fixed inner member in slp-fit frictional engagement with the respective adjacent surfaces of said inner member and said outer tubular insulator, and spring means biasing said movable heiical member toward the vented end of said tubular insulator.

References Cited in the file of this patent UNITED STATES PATENTS 2,591,370 Nelson et al Apr. 1, 1952 2,673,94] De Val Mar. 30, 1954 2,677,072 De Val Apr. 27, 1954 2,683,235 Roloson July 6, 1954 De Val Oct. 12, 1954 

